6th Year: The Reox Titration between Iodine and Thiosulphate

This is the third of our four redox titrations.

The data sheet for the reaction is available in the box on the right in the 6th Year folder. It should be downloaded and studied before you attempt the titration.

There is a slight 'twist' to this titration in that we initially titrate the red/brown solution of iodine to a pale yellow with thiosulphate. A few drops of a fresh starch solution is then added which turns the solution blue/black. The titration is continued until there is a colour change from blue/black to colourless.

We cannot judge with our eyes when the pale yellow turns colourless so we use starch as an indicator.

Again you may begin this expt as soo as you enter the lab on Monday afternoon. All chemicals will be on the side bench.